WO1998045034A1

WO1998045034A1 - Mixing apparatus

Info

Publication number: WO1998045034A1
Application number: PCT/AU1998/000248
Authority: WO
Inventors: Matthew Thomas Dunn; Douglas John Hargreaves; William Scott
Original assignee: Queensland University Of Technology
Priority date: 1997-04-09
Filing date: 1998-04-09
Publication date: 1998-10-15
Also published as: AUPO609997A0

Abstract

There is provided proportional mixer apparatus for water and soluble oil comprising a venturi assembly (14) and a control assembly (15). The venturi assembly reduces the pressure in mixing chamber (17) coupled to the control assembly (15) by a soluble oil conduit (21) supplied from a reservoir (23). The control assembly (15) comprises a piston and seal assembly (25) operating a tapered metering needle (27) governed by both the pressure in the major fluid flow line sensed through port (32) and the depression in the mixing chamber sensed at port (35), against spring (36). The needle (27) cooperates with the fixed aperture of a metering body (37) to regulate soluble oil flow. An adjuster assembly (46) adjusts the relative positions of the needle (27) and metering body (37) for a given composition across the range of water flow rates.

Description

MIXING APPARATUS This invention relates to a mixing apparatus. This invention has particular but not exclusive application to a mixing apparatus for production of emulsions for longwall mining equipment, and for illustrative purposes reference will be made to such application. However, it is to be understood that this invention could be used in metering/mixing systems that are designed to add one fluid to another at a specified ratio. In the longwall mining industry, oil and water emulsions are used as hydraulic fluids and lubricants. The make up of these emulsion are generally between 95/5 and 98/2 ratio by volume of water and a soluble oil which may be selected from a mineral or a synthetic based lubricant. Metering/mixing systems used in the mining industry have been adapted and modified from applications in other industries . The most common systems used are gear pump/gear motor, venturi type, proportioning piston and pump systems. The gear pump/gear motor system consists of a gear pump coupled to a gear motor. The oil supplied to the motor from the pump is directly proportional to the speed of the motor. This unit is designed for a fixed mixture ratio and is limited by not being able to readily change the mixture ratio. This system is also subject to wear which may cause variation in mixing ratio.

The venturi mixer is the most simple mixer unit available. The flow rate of the emulsifying oil into the main supply water depends on the flow rate of the water through the venturi. The flow through the venturi governs the suction pressure at the throat. The system consists of a venturi with a metering disk in the suction line to allow for various concentrations.

The systems do suffer from a lack of control as any change in the operating conditions results in varying concentration levels in the mixture. The initial concentration is set by the size of the orifice in the metering disk at a set system pressure. A higher main stream flow rate causes a decrease in concentration and lower main stream flow rate causes a higher concentration. This occurs if there are any fluctuations in the system supply pressure.

In venturi systems, the main fluid flow or additive inlet flow can be controlled by using a constant flow control valve. However such valves limit flow rate and it is not possible to achieve higher flow rates and maintain a constant concentration.

Proportional piston mixers operate using multistage pistons that meters the required amount of the concentrate from the metering chamber into a fresh water chamber. Each stroke of the piston delivers the mixed fluid into the reservoir. Filtration of this system is very important as contamination that enters the chambers may cause seizure due to the close tolerances between the piston and cylinder. These units suffer from an inability to make up sufficient fluid to overcome large system losses. The output ratio may be affected by any leakage past the piston in each of the chambers of the unit and there is no allowance for regulation of the final concentration in these systems. Metering pumps are used when liquid additives need to be fed into a main stream. They usually operate with two separate motor and pump sets, one for the main supply and the other for the concentrate. Mixing takes place in a mixing chamber when the two liquids come into contact. A common problem associated with normal pumps is that leakage can occur between the shaft and seal. In the pumping of toxic chemicals this cannot be tolerated. Hydraulic pumps (and motors) are extremely susceptible to variations in the properties and the quality of the fluids handled, as they are relying on close running tolerances between the surfaces in relative motion.

The mixing ratio of the fluids must be precise for their application in the mining industry. These various apparatus abovementioned are limited in their application to vary the desired concentration of the output mixture and to maintain a consistency in concentration if there is any change in operation conditions.

The present invention aims to alleviate at least one of the foregoing disadvantages and to provide mixing apparatus which will be reliable and efficient in use. Other objects and advantages of this invention will hereinafter become apparent. With the foregoing and other objects in view, this invention in one aspect resides broadly in mixing apparatus including: a pressurized fluid supply passing through a venturi; a mixing fluid supply in fluid communication with said venturi; and a control means for said mixing fluid supply, said control means being responsive to both the pressure of and the rate of flow of said pressurized fluid.

Preferably, the control means is substantially operable by the energy inherent in the pressurized fluid flow whereby the major disadvantage of driven pumps in their need for an external power supply to drive the pumps is avoided.

The control means may regulate the amount by volume of mixing fluid supplied to the venturi to be mixed with the pressurized fluid to produce an output mixture of a selected composition. The desired mixing fluid concentration in the output mixture may be maintained over a range of system pressures and fluid flow rates.

Alternatively, the control means may regulate the amount of mixing fluid to provide a controlled variation of composition with flow rate. For example, the control means may be adapted to provide a richer or leaner mix when directly feeding hydraulic apparatus, the composition being calibrated against flow rate, pressure or other characteristic.

The control means may respond to flow rate by any suitable means. For example, the control means may respond to volume rate of flow by means of a paddle wheel transducer, or may respond to venturi pressure. The control means may control the flow of the mixing fluid from a pressurized head. Alternatively, the mixing fluid may be transported to said venturi by depression therein.

The control means may comprise metering means such as a variable orifice or valve, operable by the aforementioned means responsive to pressure and flow of said pressurized fluid. For example, the control means may comprise a transducer assembly responsive to venturi and supply pressures and operating a metering assembly disposed in a delivery line for the mixing fluid. Alternatively, the control means may comprise a piston or diaphragm assembly movable in response to variation in the venturi depression and supply pressure and adapted to operate a metering assembly disposed in the mixing fluid delivery line. The metering means may comprise any suitable means that will alter the flow rate of the mixing fluid. This may include any apparatus that will alter the volume of the mixing fluid flow path. For example, these apparatus may include a pinch valve, a butterfly valve or the like.

The metering means may comprise a variable orifice or jet. The metering means may, for example, be a tapered metering needle and the variable position of the needle in the orifice may change the area of the orifice, hence the flow rate of the mixing fluid.

The amount of mixing fluid added to the pressurized fluid supply may be adjusted to various levels using an adjustment means. Consequently, the adjustment means may set the concentration of the output mixture to a specific desired level. The adjustment means may set the desired concentration by enabling a specific flow rate of the mixing fluid for a given pressurized fluid flow rate.

The adjustment means may comprise any suitable means that may adjust the volume of flow path of the mixing fluid. For example, the adjustment means may be any apparatus that may restrict or enlarge the path of flow of the mixing fluid. Alternatively, the adjustment means may adjust the metering means to set a specific area of flow therethrough for the mixing fluid. The adjustment means may set the orifice to a specified position in relation to the tapered needle or vice versa. Due to the profile and position of the tapered needle in the orifice, the area of the orifice may increase or decrease, hence the flow rate of the mixing fluid may increase or decrease accordingly. The adjustment means may be operated by a manual means or an automatic means. The manual adjustment means may require the operator to adjust the volume of the flow path. The automatic means may comprise any apparatus that may automatically sense and alter the volume of the flow path. For example, the automatic means may include an electro-pneumatic controller that controls the position of the orifice automatically using various sensing devices in combination with a monitoring system. Whilst the adjustment means may set the output mixture to a specified concentration at a given flow rate, the control means may control the supply of the mixing fluid to maintain that output mixture at that desired concentration, within a specified level, at variable pressurized fluid flow rates. The control means may further include any suitable means for calibrating the metering means, after the mixing fluid flow rate has been set to a specific level by the adjustment means, to regulate flow therethrough if there is any variation in the pressurized fluid flow rate. This may include a device which will correct the flow rate of the mixing fluid in response to an increase or decrease in the pressurized fluid flow rate.

For example, the control means may include a tensioning means which may alter the area of the orifice in the metering means in response to the pressurized fluid flow rate and system pressure. The tensioning means may retract or release the valve in the orifice.

The position of the valve may be determined from the balance of the force produced by the suction pressure in the venturi and the force produced as the tensioning means is compressed. The greater the flow rate of the pressurized fluid supply past the venturi the higher the suction pressure in the venturi. The higher the suction pressure the higher the force produced on the high pressure side of the tensioning means resulting in the retraction of the valve from the orifice. This may result in an increase in the flow rate of mixing fluid to the venturi due to the change in position and profile of the valve in the orifice increasing the area of the orifice. Any leakage of mixing fluid in the control means may be drawn off and transferred back into the venturi so that the mixing operation is unaffected.

In order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a preferred embodiment of the invention and wherein:

FIG. 1 is an assembly view of a proportional mixer unit in accordance with the present invention. In the Figure there is provided proportional mixer apparatus indicated generally as 10 interposed in a major fluid flow line 11 having a flow direction indicated at 12. The major fluid is in the present embodiment substantially water. The mixed fluid exits the apparatus at 13. The proportional mixer apparatus 10 comprises two major sub assemblies comprising a venturi assembly 14 and a control assembly 15. The venturi assembly comprises an inlet 16 adapted to accelerate the flow and thereby reduce the pressure in the fluid at mixing chamber 17. The orderly exit of mixed fluid flow is achieved through the shaped venturi outlet 20. The mixing chamber 17 is coupled to the control assembly 15 by a minor fluid delivery conduit 21 incorporating a nonreturn valve assembly 22, the minor fluid in the present embodiment being a soluble oil supplied from a reservoir 23. The control assembly 15 comprises a body member 24 having mounted in respective coaxial bores therein a piston and seal assembly 25, a connecting rod 26 and a tapered metering needle 27, connected one to the other. The movement of the piston and seal assembly 25 in its respective bore is governed by the pressure in the major fluid flow line sensed at tapping 30 and transmitted to the working face of the piston and seal assembly 25 by line 31 communicating with port 32. The movement of the piston and seal assembly 25 is also governed by the depression in the mixing chamber via tapping 33, line 34 and port 35. The piston and seal assembly 25 is biased against the forces delivered by lines 31 and 34 by spring 36.

The needle 27 meters flow from the reservoir 23 by cooperation with the fixed aperture of a metering body 37 mounted in the body member 24. Soluble oil is delivered to the metering body via supply conduit 40 connecting the supply reservoir 23 with the annular space 41 through which the connecting rod 26 passes. Metered soluble oil is collected in the annular space 42 downstream of the metering body 37, and delivered to the fluid delivery conduit 21 via holes 43, annulus 44 and drilling 45.

The bore in the body member 24 housing the needle 27 and metering body 37 assembly is closed by an adjuster assembly 46 including a manual set point adjuster 47 adapted to adjust the relative positions of the needle 27 and metering body 37 for a given initial composition and thus composition across the range of water flow rates. In use, from a minimum flow rate of water and above the pressure developed at the mixing chamber 17 falls to pressures lower than atmospheric pressure, to which the reservoir 23 is vented. It will also be appreciated that the venturi pressure difference may be established between the mixing chamber 17 and the inlet pressure by establishing the reservoir 23 at the inlet pressure at 11. This causes a suction pressure to be developed in the control assembly 15 which draws the soluble oil from the reservoir 23, through the supply conduit 40, metering body 37, one way valve 22, and into the mixing chamber 17.

In the control assembly 15 the soluble oil flows between the needle 27 and the orifice of the metering body 37, the area of flow of the soluble oil being determined by the position of the needle 27, which in turn is controlled by the pressure in the water supply line 11 acting on the piston and seal assembly 25 against the bias of the spring 36. The higher the flow rate through the venturi assembly 14 the greater the inlet pressure and thus the greater force acting on the piston and seal assembly 25. The pressure on the back of the piston and seal assembly 25 is simultaneously reduced relative to the pressure on the side exposed to the inlet pressure at 11 by connection to the low pressure mixing chamber 17 by line 34, thus contributing to the force acting against the spring 36 and further opening the aperture in the metering body 37. The line 34 also provides a return path for any water passing the piston and seal assembly 25.

The apparatus of the foregoing embodiment requires no external power and has no significantly wearing mechanical parts. The apparatus maintains a constant composition of soluble oil in water over a wide range of flow rates of water. The product fluid may be accordingly provided constantly to the using apparatus substantially on demand, although in the alternative the mixed fluid may be tanked or otherwise stored.

The foregoing mixing apparatus is advantageous in that the output mixture may be set to various specified concentrations by the adjustment means. The system also maintains a constant concentration of the mixing fluid in the output mixture over a wide range of system pressures and flow rates.

It will of course be realised that while the foregoing has been given by way of illustrative example of this invention, all such and other modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as is set forth in the claims appended hereto.

Claims

1. Mixing apparatus including: a pressurized fluid supply passing through a venturi; a mixing fluid supply in fluid communication with said venturi; and a control means for said mixing fluid supply, said control means being responsive to both the pressure of and the rate of flow of said pressurized fluid.

2. Mixing apparatus according to Claim 1, wherein said pressurized fluid is water and wherein said mixing fluid is soluble oil .

3. Mixing apparatus according to Claim 2, wherein said control means is substantially operable by the energy inherent in the pressurized fluid flow.

4. Mixing apparatus according to Claim 3, wherein said control means regulates the amount by volume of soluble oil . supplied to the venturi to be mixed with the water to produce an output mixture of a selected composition across a range of system pressures and water flow rates .

5. Mixing apparatus according to Claim 4, wherein the control means responds to flow rate by reference to venturi depression.

6. Mixing apparatus according to Claim 4, wherein the control means responds to system pressure by reference to the supply pressure of said pressurized fluid.

7. Mixing apparatus according to any one of Claims 5 and 6, wherein said mixing fluid is transported to said venturi by depression therein.

8. Mixing apparatus according to any one of the preceding Claims, wherein said control means meters said mixing fluid by means of a variable orifice operable by the said means responsive to pressure and flow of said pressurized fluid.

9. Mixing apparatus according to Claim 8, wherein said means responsive to pressure and flow of said pressurized fluid comprises a piston or diaphragm assembly movable in response to variation in the venturi depression and supply pressure.

10. Mixing apparatus according to Claim 9, wherein said variable orifice comprises a tapered metering needle operated by said piston cooperating with a fixed orifice.

11. Mixing apparatus according to any one of the preceding Claims, wherein the amount of mixing fluid added to the pressurized fluid supply may be adjusted to various levels using an adjustment means.

AMENDED CLAIMS

[received by the International Bureau on 29 July 1998 (29.07.98); original claims 1-11 replaced by amended claims 1-10 (2 pages)]

1. Mixing apparatus including: a pressurized fluid supply passing through a venturi ; a mixing fluid supply in fluid communication with said venturi; and a control means for said mixing fluid supply, said control means being responsive to both the pressure of and the rate of flow of said pressurized fluid and is substantially operable by the energy inherent in the pressurized fluid flow.

2. Mixing apparatus according to Claim 1, wherein said pressurized fluid is water and wherein said mixing fluid is soluble oil.

3. Mixing apparatus according to any one of Claims 1 and 2, wherein said control means regulates the amount by volume of soluble oil supplied to the venturi to be mixed with the water to produce an output mixture of a selected composition across a range of system pressures and water flow rates.

4. Mixing apparatus according to Claim 3, wherein the control means responds to flow rate by reference to venturi depression.

5. Mixing apparatus according to Claim 3, wherein the control means responds to system pressure by reference to the supply pressure of said pressurized fluid.

6. Mixing apparatus according to any one of Claims 4 and 5, wherein said mixing fluid is transported to said venturi by depression therein.

7. Mixing apparatus according to any one of the preceding Claims, wherein said control means meters said mixing fluid by means of a variable orifice operable by the said means responsive to pressure and flow of said pressurized fluid.

8. Mixing apparatus according to Claim 7, wherein said means responsive to pressure and flow of said pressurized fluid comprises a piston or diaphragm assembly movable in response to variation in the venturi depression and supply pressure.

9. Mixing apparatus according to Claim 8, wherein said variable orifice comprises a tapered metering needle operated by said piston cooperating with a fixed orifice.

10. Mixing apparatus according to any one of the preceding Claims, wherein the amount of mixing fluid added to the pressurized fluid supply may be adjusted to various levels using an adjustment means.